This application claims priority to PCT/FR00/00614 filed Mar. 14, 2000, which claims priority to French Patent Application No. 9903669 filed Mar. 24, 1999.
The present invention relates to a novel method of preparing block copolymers, and to certain of these block copolymers.
Block copolymers are widely known. However, it is also known that it is difficult to prepare block copolymers one of whose blocks is a polyolefin (PO), especially if the desire is that the alpha-olefin should be inserted in a regular manner in order to give a stereoregular and/or regioregular copolymer. It is also known that it is (virtually) impossible to prepare block copolymers whose two blocks are polyolefins, whether crystalline or amorphous.
Yamahiro et al., Macromol. Chem. Phys. 200, 134-141 (1999), describes a process of stopped-flow polymerization for obtaining xe2x80x9ctruexe2x80x9d PP/EP block copolymers. However, the copolymers produced are limited in terms of molecular mass, since they have a molecular weight Mn of less than or equal to 16 000 and a polydispersity index of between 3.0 and 3.3. Other molecular mass characteristics are excluded by this type of technique: in particular, higher molecular masses cannot be attained, since they are a function of the polymerization time, which can only be short (of the order of from 0.1 to 0.2 s) and in any case less than the growth time of a chain; in particular, also, lower polydispersity indexes cannot be attained, since stopped-flow polymerization is not a true polymerization with living species, but comprises a large number of transfer reactions.
Therefore, there is to date no true PP/EP copolymer, with a PP block and an EP block linked together, which has a sufficient molecular mass. This PP/EP copolymer is a crystalline PO/amorphous PO copolymer, which would find advantageous application in PP/EP polymer blends. In these blends, the crystalline PP forms the continuous phase, which is modified by the addition of EP copolymer (more specifically EPR, which is elastomeric) which forms a nodular disperse phase. A true copolymer added to this blend would play a part similar to that played by an emulsifier in emulsions, improving the compatibility of the phases, and ultimately would enhance the impact/rigidity trade-off.
This same problem of difficulty in preparing xe2x80x9ctruexe2x80x9d block copolymers occurs with copolymers one of whose blocks is a block of a polar monomer, such as MMA.
The patent application EP-A-0634429 in the name of Mitsui describes the preparation of block copolymers, one block being a polyolefin and one block being derived from a vinyl, vinylidene or lactone monomer. The catalyst used is an alkyl complex of a metal from the rare earth group, with bridged cyclopentadiene rings (bridged by a dimethylsilylene group). This document describes in particular the catalyst Me2Si(2-Me3Si,4-tBuCp)2YCH(SiMe3)2, withxe2x80x94optionallyxe2x80x94a THF-type donor complexed to the metal. The copolymers obtained, however, are not satisfactory, since the polyolefin fraction represents too low a fraction of the final copolymer. Moreover, if the polydispersity values appear to be acceptable, it is only because these values are derived from the PMMA fraction, representing the quasitotality of the copolymer. Moreover, the catalysts do not in fact provide true copolymers. In effect, extensive transfer reactions (that is, the reactions which put an end to the living nature of the polymerization) lead to the formation not of true copolymers but of a mixture of homopolymers and copolymers. Moreover, the reaction times are fairly long.
The article by Yasuda et al., Tetrahedron, Vol. 51, No. 15, pp. 4563-4570, 1995, describes hydride derivatives of lanthanides in the form of a complex with bridged cyclopentadiene rings (bridged by a dimethylsilylene group), these cyclopentadiene rings carrying substituents which have a significant steric bulk (xe2x80x9cbulky substituentxe2x80x9d). This document describes in particular the hydride catalyst Me2Si(2-Me3Si, 4-Me2tBuSiCp)3YH (represented in its dimer form). These compounds are obtained in situ by hydrogenolysis of the starting alkyl derivative, and are then used for the polymerization of alpha-olefins. Although such compounds are described as having an alpha-olefin polymerization activity greater than that of the alkyl derivatives from which they are derived, the polymerization times are still very long, of the order of half a day or a day.
These hydride catalysts also have the classic disadvantage of hydrides, namely that hydride derivatives are known to be unstable and to break down rapidly at high temperature.
The search is therefore on for an effective method of preparing block copolymers: particularly, on the one hand, copolymers one of whose blocks includes a polar fraction, and, on the other hand, copolymers whose two blocks are polyolefins.
The invention accordingly provides a method of preparing block copolymers, comprising the steps of polymerizing a first monomer using an organolanthanide catalyst in which said catalyst is in the form of a hydride complex of a trivalent metal from the rare earth group, then polymerizing at least one second monomer.
In one embodiment, the hydride complex of a trivalent metal from the rare earth group has the formula I: 
which:
Cp is a cyclopentadienyl radical;
R1, identical or different at each occurrence, is a substituent of the cyclopentadienyl group and is an alkyl radical or a silicon-containing hydrocarbon radical, containing from 1 to 20 carbon atoms, and with the Cp ring to which it is linked optionally forming an indenyl or fluorenyl ring system, it being possible optionally for each R1 to be substituted;
j, identical or different at each occurrence, is an integer from 1 to 5 inclusive;
X is a divalent alkylene radical or a divalent, silicon-containing hydrocarbon radical, containing from 1 to 20 carbon atoms, optionally containing other heteroatoms such as oxygen;
y is 1 or 2;
Ln is a trivalent metal from the rare earth group, selected from Y, Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.
In one embodiment, in the formula I, X is Si(R)2 in which R is an alkyl radical having from 1 to 4 carbon atoms.
In one embodiment, in the formula I, R1 is an alkyl radical or a silicon-containing hydrocarbon radical, containing from 1 to 6 carbon atoms, which is unbubstituted, and j is 1, 2 or 3.
In one embodiment, in the formula I, R1jCp is the group 2-Me3Si, 4-Me2tBuSiCp or the group 2-Me3Si, 4-tBuCp.
In one embodiment, in the formula I, Ln is Y or Sm.
In one embodiment, the catalyst is Me2Si(2-Me3Si, 4-Me2tBuSiCp)2YH or Me2Si(2-Me3Si, 4-tBuCp)2SmH.
In one embodiment, the catalyst is racemic.
In one embodiment, the catalyst is generated in situ in the presence of at least one portion of the first monomer.
In one embodiment, the blocks are homopolymers or random copolymers.
In one embodiment, the block copolymer comprises a block of the first monomer which is an alpha-olefin and a block of the second monomer which is a vinyl, vinylidene or lactone compound.
In this embodiment, the vinyl or vinylidene compound is represented by the formula
H2Cxe2x95x90CRxe2x80x2Z
in which Rxe2x80x2 is hydrogen or an alkyl radical having from 1 to 12 carbon atoms and Z is an electron-withdrawing radical.
In this embodiment, the vinyl or vinylidene compound is an ester of an unsaturated carboxylic acid.
In this embodiment, the polyolefin is crystalline.
In one embodiment, the second monomer is polar.
In one embodiment, the method is for preparing a PO/PMMA or PO/PL copolymer.
In this embodiment, the PO block is an iPO block.
In one embodiment, the block copolymer comprises a block of the first monomer which is a first alpha-olefin and a block of the second monomer which is a second alpha-olefin.
In a variant of this embodiment, the first polyolefin is crystalline and the second polyolefin is crystalline.
In this variant, the copolymer is a PP/PE copolymer.
In another variant of this embodiment, the first polyolefin is crystalline and the second polyolefin is amorphous.
In this variant, the copolymer is a PP/EP copolymer.
In one embodiment, the PP block is an iPP block.
The invention also provides a copolymer comprising a first block of a crystalline polyolefin and a second block of an amorphous polyolefin, with the exception of a PP/EP copolymer having a molecular mass Mn of less than or equal to 16 000 and a polydispersity index of between 3 and 3.3.
In one embodiment, the copolymer is a PP/EP copolymer, particularly one in which the PP block is an iPP block.
The invention also provides a copolymer comprising a first block of a crystalline polyolefin and a second block of a crystalline polyolefin.
The invention also provides a copolymer comprising a first block of an amorphous polyolefin and a second block of an amorphous polyolefin.
In one embodiment, the blocks are homopolymers or random copolymers.
The invention is now described in greater detail in the following description.
Catalyst.
The catalyst is an organolanthanide in the form of a hydride complex of a trivalent metal from the rare earth group (bridged); advantageously it has the formula I: 
in which:
Cp is a cyclopentadienyl radical, substituted preferably in positions 2 and 4;
R1, identical or different at each occurrence, is a substituent of the cyclopentadienyl group and is an alkyl radical or a silicon-containing hydrocarbon radical, containing from 1 to 20 carbon atoms, in particular from 1 to 6 carbon atoms, optionally forming an indenyl or fluorenyl ring system with the Cp ring to which is linked, it being possible optionally for each R1 to be substituted, for example, by up to 3 halogens;
j, identical or different at each occurrence, is an integer from 1 to 5 inclusive, in particular j is 1, 2 or 3;
in particular R1jCp is the group 2-Me3Si, 4-Me2tBuSiCp, or the group 2-Me3Si, 4-tBuCp;
X is a divalent alkylene radical or a divalent, silicon-containing hydrocarbon radical, containing from 1 to 20 carbon atoms, optionally containing other heteroatoms such as oxygen, in particular of formula Si(R)2 where R is an alkyl radical having 1 to 4 carbon atoms, in particular SiMe2;
y is 1 or 2, preferably 1;
Ln is a trivalent metal from the rare earth group, selected from Y, Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, in particular Y and Sm.
Examples of catalysts are Me2Si(2-Me3Si, 4-Me2tBuSiCp)2YH and Me2Si(2-Me3Si, 4-tBuCp)2SmH.
The catalyst may in fact have ligands which are similar to those found for the catalysts known as xe2x80x9cgroup IVxe2x80x9d or metallocene or Kaminsky catalysts. A restricted geometry may also be envisaged, and also ligands other than those described above in relation with the formula I.
In one variant, the catalyst is in a racemic form. This form makes it possible to obtain isotactic polymers.
The catalysts of the invention in hydride form are prepared, for example, by hydrogenation from the alkyl precursor, for example by application of molecular hydrogen. The alkyl precursors are described, for example, in the document EP-A-0634429 in the name of Mitsui. This operation may be performed by dissolving the alkyl starting product in a solvent (aliphatic or aromatic hydrocarbon) or suspending it in a nonsolvating hydrocarbon (aliphatic or aromatic hydrocarbon), followed by contact with molecular hydrogen.
Polymerization Method
The polymerization is very effective in particular with the catalyst formed in situ in the presence of the monomer. The proof of this efficacy is the exothermicity of the reaction mixture when the hydrogen is introduced, thereby demonstrating that the polymerization reaction is initiated immediately. Accordingly, each alkyl precursor leads to a potentially polymerizing hydride species, which leads effectively to a polymerization. In the case of the preparation of copolymers, this formation in situ in the presence of the monomer is not necessary; it is, however, preferred.
The method may be implemented with or without solvent. In the case without solvent, it is the liquid monomer itself which plays this part. In the case with solvent, the monomer (in solution or in suspension) may be in gaseous, liquid or solid form.
The polymerization medium may therefore be a solvent, mass or gaseous medium.
The solvent, when used, may be an aliphatic or aromatic hydrocarbon, such as toluene.
The reaction temperature is generally between xe2x88x9278xc2x0 C. and 150xc2x0 C., preferably from 0 to 100xc2x0 C.
The reaction pressure is generally between standard pressure and 200 bar, preferably between 1 and 20 bar.
The reaction time is generally between a few seconds and a few hours.
The monomer (or monomer mixture) may be added in one go or gradually, in a controlled way.
The above conditions apply to the polymerization steps in the case both of homopolymers and copolymers, and even of terpolymers (or more if necessary).
In the case where copolymers are prepared, the second monomer is added, for example, directly to the reaction mixture from the first step. If a solvent has been used during this step, it may either be retained or removed by customary techniques, taking care not to degrade the living species carrying the polyolefinic chain from the first step, and optionally replaced by another solvent.
The present polymerization method is efficient in that:
it makes it possible to generate poly-alpha-olefins of controlled mass, by limiting the transfer reactions
the poly-alpha-olefin species is living and in a second step is able to polymerize another monomer (olefinic, vinylic, etc.), in order to lead to the corresponding block copolymer.
The reaction scheme is as follows (where Mxe2x80x94H signifies the organolanthanide catalyst in hydride form).
Reaction 1 (generation of a (living) polyolefin)
Mxe2x80x94H+n(CH2xe2x95x90CHR)xe2x86x92Mxe2x80x94CH2xe2x80x94CRxe2x80x94(CH2xe2x80x94CHR)nxe2x88x921xe2x80x94H
There is therefore maximum avoidance of the transfer reaction which produces the following final polymer species:
xe2x80x83Mxe2x80x94H+CH2xe2x95x90CRxe2x80x94(CH2xe2x80x94CHR)nxe2x80x94H
Reaction 2 (addition to the living, growing polyolefin of the second monomer, to give the block copolymer, with limitation of the transfer reaction)
Mxe2x80x94CH2xe2x80x94CRxe2x80x94(CH2xe2x80x94CHR)nxe2x88x921xe2x80x94H+m(CH2xe2x95x90CHRxe2x80x2)xe2x86x92Mxe2x80x94CH2xe2x80x94CRxe2x80x2-(CH2xe2x80x94CHRxe2x80x2)mxe2x88x921xe2x80x94(CH2xe2x80x94CHR)nxe2x80x94H
Advantageously, the temperature of the reaction mixture will be controlled. In order to do this, it will be possible to supply the reactor continuously with the monomer; this will make it possible in particular to limit the initial exothermicity.
In the case where it is desired to obtain copolymers, the first step will be implemented under conditions similar to those for the homopolymers, and then the second monomer will be added to the reaction mixture still containing a living species.
The (co)polymers thus obtained are separated by conventional techniques.
Polymers Prepared in the Invention.
The polymers prepared as claimed in the invention may be homopolymers or random copolymers (the two or more monomers being present simultaneously in the reaction mixture) or may be blocked copolymers, or even terpolymers or more if necessary.
The homopolymer, or one copolymer block, may be isotactic, particularly when the catalyst is in a racemic form (and when the monomer is prochiral).
Examples of homopolymers are poly-alpha-olefins, the olefin containing for example from 3 to 20 carbon atoms. Examples of olefins are propylene, 1-butene, 1-hexene, 1-heptene, 1-octene, 1-decene, etc.
Examples of random copolymers are the copolymers of the above olefins, or copolymers based on ethylene.
Examples of block copolymers are copolymers containing a block of the first monomer, which is an alpha-olefin, and a block of the second monomer, which is a vinyl, vinylidene or lactone compound.
Examples of vinyl or vinylidene compounds are represented by the formula H2Cxe2x95x90CRxe2x80x2Z, in which Rxe2x80x2 is hydrogen or an alkyl radical having from 1 to 12 carbon atoms and Z is an electron-withdrawing radical.
Examples of such groups are the esters of an unsaturated carboxylic acid, especially (meth)acrylic acid. Mention may be made of methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate and phenyl methacrylate.
Examples of lactones include the cyclic esters possessing from 3 to 10 carbon atoms, and are preferably propyllactone, valerolactone and caprolactone.
The polyolefin (PO) block may be crystalline, whereas the block of the second monomer may be polar.
Specific examples of such copolymers are the copolymer PO/PMMA, especially iPO/PMMA, and PO/PL (polylactone) copolymer, especially iPO/PL.
Examples of block copolymers are copolymers containing a block of the first monomer, which is a first alpha-olefin, and a block of the second monomer, which is a second alpha-olefin.
Such examples of copolymers include in particular those in which the first polyolefin is crystalline and the second polyolefin is crystalline, especially a PP/PE copolymer.
Such examples of copolymers include in particular those in which the first polyolefin is crystalline and the second polyolefin is amorphous, especially a PP/EP copolymer.
The above PP block is, for example, an iPP block.
The invention also provides copolymers which are xe2x80x9ctruexe2x80x9d block copolymers, in contradistinction to the copolymers of the prior art, which provides copolymers which are mixtures.
The molecular weight of the homopolymers or copolymers may vary within a wide range, between 500 and 108, preferably between 5 000 and 106. The ratio, in one copolymer, between the monomers A and B may also vary within a very wide range, from 99/1 to 1/99.
The invention therefore also provides copolymers as described above.
In particular, the invention provides block copolymers of the PP/EP (crystalline PO/amorphous PO) type, with the exception of those described in the publication Yamahiro et al., Macromol. Chem. Phys. 200, 134-141 (1999), namely in particular those whose molecular weight Mn is less than or equal to 16 000 and whose polydispersity index is between 3.0 and 3.3. The invention therefore provides in particular block copolymers of the PP/EP type with a molecular weight greater than 16 000, in particular greater than 20 000, especially greater than 50 000, and copolymers of the PP/EP type whose polydispersity index is less than 3, in particular less than 2.5, especially less than 2.
The examples which follow illustrate the invention without limiting it.
Preparation of Complex 1: Me2Si(2-Me3Si, 4-tBu C5H2)2Sm(THF)2
A solution of Me2Si(2-Me3Si, 4-tBu C5H3)2 (3.01 g, 6.77 mmol) in 60 ml of THF is admixed with 8.2 ml of a 1.66M solution of nBuLi in hexane, i.e., 13.5 mmol, at 0xc2x0 C. Following reaction of the mixture at ambient temperature for 6 h with stirring, 20 ml of a 0.68M solution of tBuOK in THF, 13.6 mmol, are added. The mixture is refluxed for 12 h and the solution is evaporated to dryness. The product is washed with twice 30 ml of hexane, leading to the potassium disalt of Me2Si(2-Me3Si,4-tBu C5H3)2 in the form of white powder (yield=70%). A suspension of 5.64 g (10.8 mmol) of the potassium disalt of Me2Si(2-Me3Si, 4-tBu C5H3)2 in 80 ml of THF and 10 mmol of SmI2 in 80 ml of THF are added at the same time to 40 ml of THF at xe2x88x9280xc2x0 C. The reaction mixture is then refluxed for 12 h and the solution is subsequently evaporated to dryness. 50 ml of toluene are added to the residue and the solid obtained is separated by centrifuging. Following removal of the solvent under vacuum, the residue is extracted with twice 15 ml of THF. Recrystallization from a THF/hexane mixture leads to 1 in the form of a violet solid (yield=35%).
Preparation of Complex B: Me2Si(2-Me3Si, 4-Me2, tBuSiC5H2)2YCH(SiMe3)2 
A solution of Me2Si(2-Me3Si, 4-Me2, tBuSi C5H2)2YCl2Li(THF)2 (2 g, 2.3 mmol) in 60 ml of toluene is admixed with 4.5 ml of a 0.79M solution of (Me3Si)2CHLi in Et2O, i.e., 3.5 mmol, at 0xc2x0 C. The mixture is stirred from 0xc2x0 C. to ambient temperature for 13 hours, after which the solvent is evaporated under vacuum. 80 ml of hexane are added to the residue and the suspension is stirred for 24 hours. The insoluble solid is recovered by centrifuging and is recrystallized from hexane to give Bxe2x80x94yield=36%.
Preparation of Complex C: Me2Si(2-Me3Si, 4-tBuSi C5H2)2SmCH(SiMe3)2
A solution of Me2Si(2-Me3Si, 4-tBu C5H2)2SmCl2Li(THF)2 (2.3 mmol) in 60 ml of toluene is admixed with 4.5 ml of a 0.79M solution of (Me3Si)2CHLi in Et2O, i.e., 3.5 mmol, at 0xc2x0 C. The mixture is stirred from 0xc2x0 C. to ambient temperature for 13 hours, after which the solvent is evaporated under vacuum. 80 ml of hexane are added to the residue and the suspension is stirred for 24 hours. The insoluble solid is recovered by centrifuging and is recrystallized from hexane to give Cxe2x80x94yield=28%.